1. Field of the Invention
Exemplary aspects of the present invention generally relate to a cleaning device employed in an image forming apparatus such as a copying machine, a facsimile machine, and a printer; a process cartridge; and an image forming apparatus that includes the cleaning device and the process cartridge.
2. Discussion of the Background
A related-art image forming apparatus, such as a copying machine, a facsimile machine, a printer, or a multifunction printer having two or more of copying, printing, scanning, and facsimile functions, forms a toner image on a recording medium (e.g., a sheet) according to image data using an electrophotographic method. In such a method, for example, a charger charges a surface of an image bearing member (e.g., a photoconductor). An optical device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data. The electrostatic latent image is developed with a developer (e.g., a toner) to form a toner image on the photoconductor. A transfer device transfers the toner image formed on the photoconductor onto a sheet. A fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus.
The related-art image forming apparatus further includes a cleaning device for removing toner particles remaining on a surface of the photoconductor after transfer has been performed. The cleaning device includes a cleaning blade formed of rubber, which contacts the photoconductor to remove the toner particles remaining on the surface of the photoconductor. When the cleaning blade does not accurately contact the photoconductor, the toner particles on the surface of the photoconductor pass through the cleaning blade and remain thereon, degrading cleaning performance. To solve such a problem, the cleaning blade is pressed against the photoconductor with a high linear pressure. However, the high linear pressure causes curling-up of the cleaning blade. As a result, a part of the toner particles are not removed by the cleaning blade and remain on the surface of the photoconductor in a linear or band-like shape. Thus, higher cleaning performance may not be stably obtained. Moreover, over an extended period of time, the surface of the photoconductor is further worn away, shortening a product life of the photoconductor.
To meet demand for higher quality images, toner particles having a smaller particle diameter and a spherical shape have been developed in recent years. Furthermore, to meet demand for reduction in manufacturing costs of toner and improvement in transfer rate, image forming apparatuses using toner having particles of a spherical shape manufactured using a polymerization method have become widely commercialized over those using pulverized toner having particles of an irregular shape. At the same time, however, it is known that the cleaning blade cannot reliably remove the toner particles having a smaller particle diameter and a spherical shape from the surface of the photoconductor as compared to pulverized toner particles.
One example of a cleaning device uses an electrostatic brush cleaning method to reliably remove the toner particles having a smaller particle diameter and a spherical shape from the surface of the photoconductor, and to prevent the surface of the photoconductor from being abraded by mechanical rubbing by the cleaning blade. In the electrostatic brush cleaning method, a cleaning brush is provided in contact with the surface of the photoconductor, and furthermore, a collecting roller serving as a cleaning member is provided in contact with the cleaning brush to remove the toner particles from the cleaning brush. A voltage is applied to the cleaning brush, or to both of the cleaning brush and the collecting roller. The toner particles charged to a polarity opposite to that of the voltage applied to the cleaning brush are electrostatically adhered to a brush string of the cleaning brush, so that the toner particles are removed from the surface of the photoconductor. Therefore, the electrostatic brush cleaning method can provide reliable and improved cleaning performance for the toner particles having a smaller particle diameter and a spherical shape.
Generally, a voltage with a polarity opposite to that of toner particles after development has been performed is applied to a transfer member so as to transfer the toner particles on the surface of the photoconductor onto a sheet. Therefore, a charge with a polarity opposite to that of the charge injected into the toner particles during development is injected into the toner particles on the surface of the photoconductor during transfer. Consequently, the more weakly charged toner particles are charged to the polarity opposite to that of the toner particles after development has been performed due to the charge injection during transfer described above. Therefore, a part of the toner particles remaining on the surface of the photoconductor after transfer has been performed have a polarity identical to that of the toner particles after development has been performed, and the other part of the toner particles have a polarity opposite to that of the toner particles after development has been performed. In other words, both toner particles charged to the polarity opposite to that of the voltage applied to the cleaning brush and toner particles charged to the polarity identical to that of the voltage applied to the cleaning brush remain on the surface of the photoconductor after transfer has been performed. Consequently, the toner particles on the surface of the photoconductor that are charged to the polarity identical to that of the voltage applied to the cleaning brush are not electrostatically adhered to the cleaning brush and pass through the cleaning brush, resulting in poor cleaning performance.